Salicylic acid enhances antifungal resistance to Magnaporthe grisea in rice plants

Salicylic acid (SA) may play an important role in induced disease resistance in rice but its mode of action in plant defence remains unclear. In this study, we examined the effect of exogenous SA treatment on host resistance and biochemistry of four near-isogenic lines of rice to the blast fungus Magnaporthe grisea. Host resistance, as indicated by suppressed blast lesion formation, was enhanced following foliar application of 8 mM SA in the two isogenic lines susceptible to the pathogen. Exogenous SA treatment increased the enzyme activity of peroxidase and polyphenol oxidase in all isogenic lines. Chemical analysis of crude leaf extracts detected higher concentrations of four rice phytoalexins (oryzalexin A, C and F and momilactone A) following root application of SA treatment. Furthermore, the hydrolysates of conjugated antifungal compounds from the SA-treated rice showed a much more potent inhibitory effect on the spore germination of M. grisea than the controls from the untreated plants, suggesting the existence of inducible conjugated antifungal compounds. Taken together, these data demonstrate that exogenous SA treatment of rice could increase production of the enzymes implicated in resistance to oxidative stresses and antifungal compounds, which appear to play a significant role in rice resistance to the invasion of blast fungal pathogens.